An electronic amplifier (amplifier, amp) is an apparatus that enables an input electrical signal to control power from a source independent of the signal and thus is capable of delivering an output that bears some relationship to, and is generally greater than, the input signal. An amplifier may be designed for a specific purpose. For example, radio frequency (RF) amplifiers may convert low-power signals with frequencies generally in the portion of the electromagnetic spectrum between audio and infrared into a larger signal with more power, typically for driving the antenna of a transmitter. In another example, an audio amplifier may amplify audio signals (e.g., signals in the range of human hearing) to a suitable level (magnitude) for driving loudspeakers or other devices. A guitar amplifier is another example of an amplifier designed for a specific purpose. A guitar amplifier is designed to amplify the electrical signal of guitar or an acoustic pickup.
An amplifier may strive to reproduce the electromagnetic spectrum (e.g., spectral characteristics, frequencies, tone) of the input signal. Alternatively, the amplifier may alter the spectrum of the input signal. The output spectrum may depend on the output power level (magnitude). For example, a guitar amplifier may add effects such as distortion at high output power levels. A musician may find these effects desirable. However, guitar amplifiers may fail to reproduce the same effects at lower output power. For example, a musician using a guitar amplifier in a concert hall or arena setting with a high power output may desire to have the same effects at a lower output power while playing in a smaller room or location. Maintaining the relationship of input to output spectrum over the dynamic range (the ratio between the largest and smallest possible values) of output power may not be achievable with typical amplifiers.
In other examples, it may be desirable for audio amplifiers to faithfully reproduce the electromagnetic spectrum of the input signal at the output regardless of output power levels. Audio amplifiers that introduce distortion or other effects alter the original spectrum (e.g., sounds) which listeners may find objectionable. In this example, it is desirable to maintain the relationship of input spectrum to output spectrum over the dynamic range of output power without distortion.
Electronic amplifiers that maintain a desired relationship of input spectrum to output spectrum over the dynamic range of output powers alleviate the problem of power output dependent spectral variations. Thus, maintaining a spectral relationship between an input and output signal in an amplifier is a need felt by many users across multiple fields.